This disclosure relates to a method and apparatus for screening a request to establish a session initiation protocol (SIP) session in an internet protocol (IP) network. For example, this disclosure describes exemplary embodiments of network nodes within the IP network that could implement a process for screening an INVITE request to establish a SIP session. However, it will be appreciated that the disclosed concepts may have usefulness in other types of SIP requests, such as ACK, PRACK, UPDATE, REFER, MESSAGE, SUBSCRIBE, and NOTIFY requests. Moreover, this disclosure describes exemplary embodiments the method and apparatus for screening a request to establish a SIP session with origination and destination end points within the IP network. However, it will be appreciated that the origination end point, destination end point, or both can be in a non-IP network.
By way of background, the Internet Engineering Task Force (IETF) has approved a new protocol for communicating resource priority by inserting an optional session initiation protocol (SIP) header field in SIP requests, such as the SIP INVITE request. The optional header field is referred to a Resource Priority Header (RPH) and includes parameters so the corresponding SIP request, such as the INVITE message, signals that this session is to be given priority treatment and the corresponding level of such treatment. For additional information on RPH, refer to RFC 4412, Communications Resource Priority for the Session Initiation Protocol (SIP), Schulzrinne et al., The Internet Society, February 2006. For additional information on the INVITE request, refer to RFC 3261, SIP: Session Initiation Protocol, Rosenberg et al., The Internet Society, June 2002. The contents of both RFC 4412 and RFC 3261 are fully incorporated herein by reference.
One application for the RPH is the Government Emergency Telecommunication Service (GETS) in the next generation network (NGN) which is in the process of being defined for deployment in the United States and other countries. The GETS application is intended to allow government authorized users to have a high probability of session completion during times of crisis when an IP network providing communication services may be highly congested because of a manmade or natural disaster. It is imperative for continuity of government, mitigation of loss of life and property, and a more rapid restoration of order that these critical communications succeed even when normal communications are failing from the congestion caused by massive attempts and possible physical damage to the IP network.
It is advantageous to insert the RPH indicator in the SIP request as early as possible to prevent the message from be discarded by the overload controls protecting the router buffers. However, allowing the user equipment (UE) to insert the RPH can lead to a denial of service attack on the IP network during its most fragile state. Concern over UE insertion have led some to propose that UE insertion of the RPH be ignored out of fear of unauthorized users and the potential for a denial of service attack. However, this solution suffers from the potential loss of some session attempts from UE's in congested areas that are being dropped by congestion control mechanisms prior to reaching a network node that can insert the RPH for the caller.
Based on the foregoing, a solution that reduces the risk of a denial of service attack due to early insertion of the RPH, including UE insertion, is desirable. Additionally, a solution that operates on high volumes of traffic and high congestion by exception is desirable so that session processing is not burdened during low or medium congestion.